The present invention relates to disc drive systems and more particularly for devices for a write to read switching circuit.
Magnetic disc drives have read/write heads out of which the write head portion is used for writing data to magnetic discs and the read head portion is used for reading data from the magnetic disc. During a write operation, a write signal is provided to a selected write head from a write control circuit. The write signal represents data to be encoded into the magnetic disc. More particularly, the write head receives encoded digital data from a xe2x80x9cchannelxe2x80x9d circuit. The transitions of the signal received from the channel circuit causes the write current flowing within the write head to reverse direction which in turn, induces a flux reversal in the magnetized material of the medium of the magnetic disc.
During a read operation, the read head senses flux reversals from the magnetic disc. The flux reversals are encoded into magnetic disc during the write operation. Based on the flux reversals, the read head provides a read signal to a read channel. The read circuit amplifies the read signal, and the channel circuit recovers the data. The read circuit then provides the data to a magnetic disc controller for further processing.
Each magnetic disc in a disk drive has a corresponding xe2x80x9cheadxe2x80x9d adjacent to the top and bottom surface of the disc. Thus, there are two heads per stack where N equals the number of disc in a drive. Normally, only one head is active at a given time in order to control these channels. Typically, each channel additionally includes a current path for current to flow to the MR head.
When switching from a write mode when the write circuit is activated to a read mode when a read circuit is activated, a write to read switching circuit is employed to assure that the transitions created by the change from the write mode to the read mode have been eliminated. One of the criterion of a write to read switching circuit is to minimize any delay associated with the write to read switching circuit.
One such write to read switching circuit is illustrated in FIG. 1. This circuit includes a head 100, which is connected to a Rmr measurement circuit 122. The RMR measurement circuit 122 includes a resistor 124 which is coupled to a FET 126 which is coupled to ground. This FET 126 controls the activation of the measurement circuit 122. However, the FET 126 requires a finite amount of time to switch the measurement circuit 122 and introduces noise to the write to read switching circuit. Additionally, the FET 124 shuts off the current to the Rmr measurement circuit 122 during write mode. However, when going. from write to read, the current begins to flow in the Rmr measurement circuit 122 causing a transient in the head circuit 100. This results in a longer time for the current to settle in the Rmr measurement circuit 122 causing additional delay in the write to read time.
Additionally, FIG. 1 illustrates transconductance circuit 114. The lower corner frequency of the reader Fcf is set by two poles namely, Gmxe2x88x92c and low pass filter pole PLPF. These multiple poles with a zero results in the read circuit being less stable causing over shoot, and the transient response of the reader circuit is extended. This over shoot causes substantially larger settling time with the reader resulting in poor write to read time.
Additionally, there is a further problem associated with the transconductance circuit 114. As illustrated in FIG. 1, reference voltage generator 118 output a voltage Vref to transconductance circuit 114. The transconductances circuit 114 inputs and references the reference voltage Vref with respect to internal ground. In contrast, the external resistor 120 is connected to external ground. As a consequence, when the preamplifier goes from a write to read, there is a transient voltage generated in the internal ground. This will alter the voltage Vref which is measured with respect to internal ground. The transient affects the generation of the transconductance circuit 114. Any change in voltage Vref will cause a transient in current I which flows from transconductance circuit 114 to capacitor 116 and to the gate of transistor 102.
The present invention includes a write to read switching circuit having a switching time of 200 nano seconds. This is because by the invention, the transients which are generated by switch from the write mode to the read mode are significantly reduced. The write to read switching circuit of the present invention eliminates the low pass filter which is connected to a transconductance circuit. Additionally, the present invention eliminates a switch in the Rmr measurement circuit and provides a switchless Rmr measurement circuit. Furthermore, the present invention provides a write to read switching circuit which only uses a internal ground as a reference. More specifically, the write to read switching circuit is directly connected to internal ground through a resistor which is connected to the reference voltage generator.